Original Medicare, Medicare Advantage, and Medigap: The Three Paths

Once you’re eligible for Medicare, you’re really choosing between three structures, not two:

• Original Medicare (Parts A & B): Run directly by the federal government. You can see any provider nationwide that accepts Medicare, but it doesn’t cap your out-of-pocket costs on its own.
• Medicare Advantage (Part C): Private insurance that bundles Parts A and B (and usually Part D drug coverage) into one plan, typically with a network of providers and often extras like dental or vision.
• Medicare Supplement / Medigap: A private policy that pairs with Original Medicare to help cover the cost-sharing gaps — deductibles, copays, coinsurance — that Original Medicare leaves you responsible for.

You generally choose Medicare Advantage or a Medigap policy, not both, since Medigap is built to supplement Original Medicare rather than a Medicare Advantage plan.

Medicare Advantage vs. Medicare Supplement: The Core Tradeoff

The decision usually comes down to one tradeoff: network and cost versus flexibility and predictability.

Medicare Advantage plans often have a low or even $0 monthly premium and bundle in extra benefits, but you’re typically limited to a network of providers, and costs can be less predictable if you need significant care during the year.

Medicare Supplement (Medigap) plans usually carry a higher monthly premium, but in exchange you can see any provider nationwide who accepts Medicare, with no network restrictions, and your out-of-pocket costs during the year are far more predictable since the policy is filling in the gaps Original Medicare leaves.

Know Your Enrollment Windows

Medicare has more enrollment windows than most people expect, and each one does something different:

• Initial Enrollment Period: A 7-month window — 3 months before your 65th birthday month, your birthday month, and 3 months after.
• Annual Open Enrollment Period: October 15 – December 7 every year. Switch between Original Medicare and Medicare Advantage, or change/join/drop a Part D drug plan.
• Medicare Advantage Open Enrollment Period: January 1 – March 31 every year, but only if you’re already enrolled in a Medicare Advantage plan — lets you switch to a different MA plan or move back to Original Medicare.
• Medigap Open Enrollment Period: A one-time 6-month window that starts the first day of the month you’re both 65+ and enrolled in Part B.

Why Timing Your Medigap Enrollment Matters Most

Of all of these, the Medigap window is the one to pay closest attention to. During your one-time 6-month Medigap open enrollment period, insurers have to sell you a policy regardless of any health conditions you have, with no medical underwriting. Miss that window, and insurers in most states can require medical underwriting later, which means a health condition could get you charged more, or in some cases denied coverage outright. If a Medicare Supplement plan is something you’re considering, timing that first enrollment correctly matters more than almost anything else in the decision.

Which Fits Your Situation?

• Budget-conscious and comfortable with a network: Medicare Advantage is usually the more affordable starting point, especially with a $0-premium option available in many areas.
• Travel often, or want to keep your current doctors regardless of network: A Medicare Supplement plan generally offers more flexibility since it works with any provider that accepts Medicare.
• Not sure, or turning 65 soon: This is exactly the kind of decision worth talking through with a licensed agent before you enroll, since the Medigap timing question in particular is hard to undo later.

Frequently Asked Questions